As is known in the art, syringes are medical delivery devices utilizable to administer a medicament to a patient. Syringes are normally provided in prefillable form, wherein a set dosage of medicament can be filled into the syringe by a pharmaceutical manufacturer for distribution to the end user, or they are empty and intended to be filled by the end user from a vial or other source of medicament at the time administration of the medicament is desired.
Syringes typically include a barrel portion adapted to retain the medicament. The distal end of the barrel is normally configured to mate with a conventional piercing element, such as a pointed needle cannula made of steel or like material or a blunt ended cannula formed of plastic, to deliver the medicament contained in the barrel. A plunger rod is inserted through the open distal end of the syringe barrel and, through its engagement with an elastomeric or rubber-like stopper element fitted in a fluid-tight manner within the interior of the barrel, a user can apply manual force to the plunger to deliver the medicament through the piercing element.
More typically the case with pointed needle cannulae, accidental needle sticks that occur after the needle cannula has been used generally pose a greater health risk. To avoid such accidents, many prior art hypodermic syringes include a rigid cylindrical safety shield telescoped over the syringe barrel. The prior art safety shield can be slid from a proximal position where the needle cannula is exposed for use, to a distal position where the safety shield protectively surrounds the needle cannula.
Most prior art hypodermic syringes with cylindrical safety shields telescoped over the syringe barrel include structure for locking the safety shield in its distal position. Examples of such structures are found, for instance, in U.S. Pat. Nos. 5,342,309 and 5,385,555 to Hausser and U.S. Pat. No. 5,304,149 to Morigi.
While generally suitable for the tasks employed, further improvements are still being sought. For instance, where the syringe is prefillable by a pharmaceutical manufacturer, it would be beneficial to incorporate improvements into the locking structure employed with the safety shields to better facilitate a pharmaceutical manufacturer's processing of the various components associated with the syringe barrel and safety shield. These improvements should also facilitate the end user's normal use of the prefillable syringe and easy activation of the safety shield once safe disposal of the syringe is desired. Moreover, most of the prior art approaches focus their efforts on employing a plastic collar element on some distal portion of the syringe barrel, with the shield locking onto the collar. While a valid approach, because many of the prefilled syringes currently in use are made of glass, it can be difficult to assemble the plastic collar element onto the syringe barrel. Accordingly, it would be useful to design a structure whereby the collar were incorporated as part of the shield structure itself.